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https://www.readbyqxmd.com/read/28736581/the-remarkable-amphoteric-nature-of-defective-uio-66-in-catalytic-reactions
#1
Julianna Hajek, Bart Bueken, Michel Waroquier, Dirk De Vos, Veronique Van Speybroeck
One of the major requirements in solid acid and base catalyzed reactions is that the reactants, intermediates or activated complexes cooperate with several functions of catalyst support. In this work the remarkable bifunctional behavior of the defective UiO-66(Zr) metal organic framework is shown for acid-base pair catalysis. The active site relies on the presence of coordinatively unsaturated zirconium sites, which may be tuned by removing framework linkers and by removal of water from the inorganic bricks using a dehydration treatment...
June 22, 2017: ChemCatChem
https://www.readbyqxmd.com/read/28670348/proton-reduction-reaction-catalyzed-by-homoleptic-nickel-bis-1-2-dithiolate-complexes-experimental-and-theoretical-mechanistic-investigations
#2
Athanasios Zarkadoulas, Martin J Field, Vincent Artero, Christiana A Mitsopoulou
A series of homoleptic monoanionic nickel dithiolene complexes [Ni(bdt)2](NBu4), [Ni(tdt)2](NBu4), and [Ni(mnt)2](NBu4) containing the ligands benzene-1,2-dithiolate (bdt(2-)), toluene-3,4-dithiolate (tdt(2-)) and maleonitriledithiolate (mnt(2-)), respectively, have been employed as electrocatalysts in the hydrogen evolution reaction with trifluoroacetic acid as proton source in acetonitrile. All complexes were active catalysts with TONs reaching 113, 158 and 6 for [Ni(bdt)2](NBu4), [Ni(tdt)2](NBu4), and [Ni(mnt)2](NBu4), respectively...
June 22, 2017: ChemCatChem
https://www.readbyqxmd.com/read/28706570/the-effects-of-secondary-oxides-on-copper-based-catalysts-for-green-methanol-synthesis
#3
James S Hayward, Paul J Smith, Simon A Kondrat, Michael Bowker, Graham J Hutchings
Catalysts for methanol synthesis from CO2 and H2 have been produced by two main methods: co-precipitation and supercritical anti-solvent (SAS) precipitation. These two methods are compared, along with the behaviour of copper supported on Zn, Mg, Mn, and Ce oxides. Although the SAS method produces initially active material with high Cu specific surface area, they appear to be unstable during reaction losing significant amounts of surface area and hence activity. The CuZn catalysts prepared by co-precipitation, however, showed much greater thermal and reactive stability than the other materials...
May 10, 2017: ChemCatChem
https://www.readbyqxmd.com/read/28706569/supercritical-antisolvent-precipitation-of-amorphous-copper-zinc-georgeite-and-acetate-precursors-for-the-preparation-of-ambient-pressure-water-gas-shift-copper-zinc-oxide-catalysts
#4
Paul J Smith, Simon A Kondrat, James H Carter, Philip A Chater, Jonathan K Bartley, Stuart H Taylor, Michael S Spencer, Graham J Hutchings
A series of copper-zinc acetate and zincian georgeite precursors have been produced by supercritical CO2 antisolvent (SAS) precipitation as precursors to Cu/ZnO catalysts for the water gas shift (WGS) reaction. The amorphous materials were prepared by varying the water/ethanol volumetric ratio in the initial metal acetate solutions. Water addition promoted georgeite formation at the expense of mixed metal acetates, which are formed in the absence of the water co-solvent. Optimum SAS precipitation occurs without water to give high surface areas, whereas high water content gives inferior surface areas and copper-zinc segregation...
May 10, 2017: ChemCatChem
https://www.readbyqxmd.com/read/28580035/acetic-acid-ketonization-over-fe3o4-sio2-for-pyrolysis-bio-oil-upgrading
#5
James A Bennett, Christopher M A Parlett, Mark A Isaacs, Lee J Durndell, Luca Olivi, Adam F Lee, Karen Wilson
A family of silica-supported, magnetite nanoparticle catalysts was synthesised and investigated for continuous-flow acetic acid ketonisation as a model pyrolysis bio-oil upgrading reaction. The physico-chemical properties of Fe3O4/SiO2 catalysts were characterised by using high-resolution transmission electron microscopy, X-ray absorption spectroscopy, X-ray photo-electron spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy, thermogravimetric analysis and porosimetry. The acid site densities were inversely proportional to the Fe3O4 particle size, although the acid strength and Lewis character were size-invariant, and correlated with the specific activity for the vapour-phase acetic ketonisation to acetone...
May 10, 2017: ChemCatChem
https://www.readbyqxmd.com/read/28529668/diastereoselective-radical-type-cyclopropanation-of-electron-deficient-alkenes-mediated-by-the-highly-active-cobalt-ii-tetramethyltetraaza-14-annulene-catalyst
#6
Andrei Chirila, Braja Gopal Das, Nanda D Paul, Bas de Bruin
A new protocol for the catalytic synthesis of cyclopropanes using electron-deficient alkenes is presented, which is catalysed by a series of affordable, easy to synthesise and highly active substituted cobalt(II) tetraaza[14]annulenes. These catalysts are compatible with the use of sodium tosylhydrazone salts as precursors to diazo compounds in one-pot catalytic transformations to afford the desired cyclopropanes in almost quantitative yields. The reaction takes advantage of the metalloradical character of the Co complexes to activate the diazo compounds...
April 21, 2017: ChemCatChem
https://www.readbyqxmd.com/read/28706568/gold-i-mediated-thiourea-organocatalyst-activation-a-synergic-effect-for-asymmetric-catalysis
#7
Anabel Izaga, Raquel P Herrera, M Concepción Gimeno
Several group 11 metal complexes with chiral thiourea organocatalysts have been prepared and tested as organocatalysts. The promising results on the influence of metal-assisted thiourea organocatalysts in the asymmetric Friedel-Crafts alkylation of indole with nitrostyrene are described. Better results with the metal complexes have been achieved because of the cooperative effects between the chiral thiourea and the metal. The synergic effect between both species is higher than the effect promoted by each one separately, especially for gold(I)...
April 7, 2017: ChemCatChem
https://www.readbyqxmd.com/read/28515795/a-theoretical-investigation-on-co-oxidation-by-single-atom-catalysts-m1-%C3%AE-al2o3-m-pd-fe-co-and-ni
#8
Tao Yang, Ryoichi Fukuda, Saburo Hosokawa, Tsunehiro Tanaka, Shigeyoshi Sakaki, Masahiro Ehara
Single-atom catalysts have attracted much interest recently because of their excellent stability, high catalytic activity, and remarkable atom efficiency. Inspired by the recent experimental discovery of a highly efficient single-atom catalyst Pd1/γ-Al2O3, we conducted a comprehensive DFT study on geometries, stabilities and CO oxidation catalytic activities of M1/γ-Al2O3 (M=Pd, Fe, Co, and Ni) by using slab-model. One of the most important results here is that Ni1/Al2O3 catalyst exhibits higher activity in CO oxidation than Pd1/Al2O3...
April 7, 2017: ChemCatChem
https://www.readbyqxmd.com/read/28450969/characterization-of-carboxylic-acid-reductases-as-enzymes-in-the-toolbox-for-synthetic-chemistry
#9
William Finnigan, Adam Thomas, Holly Cromar, Ben Gough, Radka Snajdrova, Joseph P Adams, Jennifer A Littlechild, Nicholas J Harmer
Carboxylic acid reductase enzymes (CARs) meet the demand in synthetic chemistry for a green and regiospecific route to aldehydes from their respective carboxylic acids. However, relatively few of these enzymes have been characterized. A sequence alignment with members of the ANL (Acyl-CoA synthetase/ NRPS adenylation domain/Luciferase) superfamily of enzymes shed light on CAR functional dynamics. Four unstudied enzymes were selected by using a phylogenetic analysis of known and hypothetical CARs, and for the first time, a thorough biochemical characterization was performed...
March 20, 2017: ChemCatChem
https://www.readbyqxmd.com/read/28286582/effects-of-the-functionalization-of-the-ordered-mesoporous-carbon-support-surface-on-iron-catalysts-for-the-fischer-tropsch-synthesis-of-lower-olefins
#10
Martin Oschatz, Jan P Hofmann, Tom W van Deelen, Wouter S Lamme, Nynke A Krans, Emiel J M Hensen, Krijn P de Jong
Ordered mesoporous carbon (CMK-3) with different surface modifications is applied as a support for Fe-based catalysts in the Fischer-Tropsch to olefins synthesis (FTO) with and without sodium and sulfur promoters. Different concentrations of functional groups do not affect the size (3-5 nm) of Fe particles in the fresh catalysts but iron (carbide) supported on N-enriched CMK-3 and a support with a lower concentration of functional groups show higher catalytic activity under industrially relevant FTO conditions (340 °C, 10 bar, H2/CO=2) compared to a support with an O-enriched surface...
February 21, 2017: ChemCatChem
https://www.readbyqxmd.com/read/28239429/future-challenges-in-heterogeneous-catalysis-understanding-catalysts-under-dynamic-reaction-conditions
#11
Kai F Kalz, Ralph Kraehnert, Muslim Dvoyashkin, Roland Dittmeyer, Roger Gläser, Ulrike Krewer, Karsten Reuter, Jan-Dierk Grunwaldt
In the future, (electro-)chemical catalysts will have to be more tolerant towards a varying supply of energy and raw materials. This is mainly due to the fluctuating nature of renewable energies. For example, power-to-chemical processes require a shift from steady-state operation towards operation under dynamic reaction conditions. This brings along a number of demands for the design of both catalysts and reactors, because it is well-known that the structure of catalysts is very dynamic. However, in-depth studies of catalysts and catalytic reactors under such transient conditions have only started recently...
January 9, 2017: ChemCatChem
https://www.readbyqxmd.com/read/28163792/effect-of-feedstock-and-catalyst-impurities-on-the-methanol-to-olefin-reaction-over-h-sapo-34
#12
Charlotte Vogt, Bert M Weckhuysen, Javier Ruiz-Martínez
Operando UV/Vis spectroscopy with on-line mass spectrometry was used to study the effect of different types of impurities on the hydrocarbon pool species and the activity of H-SAPO-34 as a methanol-to-olefins (MTO) catalyst. Successive reaction cycles with different purity feedstocks were studied, with an intermittent regeneration step. The combined study of two distinct impurity types (i.e., feed and internal impurities) leads to new insights into MTO catalyst activation and deactivation mechanisms. In the presence of low amounts of feed impurities, the induction and active periods of the process are prolonged...
January 9, 2017: ChemCatChem
https://www.readbyqxmd.com/read/28450968/visible-light-controlled-oxidation-of-glucose-using-titania-supported-silver-photocatalysts
#13
Luigi Da Vià, Carlo Recchi, Thomas E Davies, Nicholas Greeves, Jose A Lopez-Sanchez
The visible-light-mediated photo-catalytic selective valorisation of glucose using TiO2-supported Ag nanoparticles is shown for the first time. The optimisation of the catalyst composition, substrate-to-catalyst ratio and reaction medium proved that a near total suppression of the mineralisation pathway could be achieved with a selectivity to partial oxidation products and small-chain monosaccharides as high as 98 %. The primary products were determined to be gluconic acid, arabinose, erythrose, glyceraldehyde and formic acid...
November 22, 2016: ChemCatChem
https://www.readbyqxmd.com/read/27917245/reactivity-of-a-ruthenium-carbonyl-complex-in-the-methanol-dehydrogenation-reaction
#14
Fenna F van de Watering, Martin Lutz, Wojciech I Dzik, Bas de Bruin, Joost N H Reek
Finding new catalysts for the release of molecular hydrogen from methanol is of high relevance in the context of the development of sustainable energy carriers. Herein, we report that the ruthenium complex Ru(salbinapht)(CO)(Pi-Pr3) {salbinapht=2-[({2'-[(2-hydroxybenzyl)amino]-[1,1'-binaphthalen]-2-yl}imino)methyl]phenolato} (2) catalyzes the methanol dehydrogenation reaction in the presence of base and water to yield H2, formate, and carbonate. Dihydrogen is the only gas detected and a turnover frequency up to 55 h(-1) at 82 °C is reached...
September 7, 2016: ChemCatChem
https://www.readbyqxmd.com/read/27867424/aldehyde-and-ketone-synthesis-by-p450-catalyzed-oxidative-deamination-of-alkyl-azides
#15
Simone Giovani, Hanan Alwaseem, Rudi Fasan
Heme-containing proteins have recently attracted increasing attention for their ability to promote synthetically valuable transformations not found in nature. Following the recent discovery that engineered variants of myoglobin can catalyze the direct conversion of organic azides to aldehydes, we investigated the azide oxidative deamination reactivity of a variety of hemoproteins featuring different heme coordination environments. Our studies show that although several heme-containing enzymes possess basal activity in this reaction, an engineered variant of the bacterial cytochrome P450 CYP102A1 constitutes a particularly efficient biocatalyst for promoting this transformation, exhibiting a broad substrate scope along with high catalytic activity (up to 11,300 TON), excellent chemoselectivity, and enhanced reactivity toward secondary alkyl azides to yield ketones...
August 22, 2016: ChemCatChem
https://www.readbyqxmd.com/read/27840663/a-dft-study-of-co2-hydrogenation-on-faujasite-supported-ir4-clusters-on-the-role-of-water-for-selectivity-control
#16
Bartłomiej M Szyja, Daniel Smykowski, Jerzy Szczygieł, Emiel J M Hensen, Evgeny A Pidko
Reaction mechanisms for the catalytic hydrogenation of CO2 by faujasite-supported Ir4 clusters were studied by periodic DFT calculations. The reaction can proceed through two alternative paths. The thermodynamically favoured path results in the reduction of CO2 to CO, whereas the other, kinetically preferred channel involves CO2 hydrogenation to formic acid under water-free conditions. Both paths are promoted by catalytic amounts of water confined inside the zeolite micropores with a stronger promotion effect for the reduction path...
August 8, 2016: ChemCatChem
https://www.readbyqxmd.com/read/27840662/copper-i-phosphinite-complexes-in-click-cycloadditions-three-component-reactions-and-preparation-of-5-iodotriazoles
#17
Juana M Pérez, Peter Crosbie, Steven Lal, Silvia Díez-González
The remarkable activity displayed by copper(I)-phosphinite complexes of general formula [CuBr(L)] in two challenging cycloadditions is reported: a) the one-pot azidonation/cycloaddition of boronic acids, NaN3, and terminal alkynes; b) the cycloaddition of azides and iodoalkynes. These air-stable catalysts led to very good results in both cases and the expected triazoles could be isolated in pure form under 'Click-suitable' conditions.
July 6, 2016: ChemCatChem
https://www.readbyqxmd.com/read/27840661/real-time-analysis-of-a-working-triethylaluminium-modified-cr-ti-sio2-ethylene-polymerization-catalyst-with-in%C3%A2-situ-infrared-spectroscopy
#18
Dimitrije Cicmil, Jurjen Meeuwissen, Aurélien Vantomme, Bert M Weckhuysen
A diffuse reflectance infrared Fourier-transform (DRIFT) study has been conducted at 373 K and 1 bar on an industrial Cr/Ti/SiO2 Phillips-type catalyst modified with, and without, triethylaluminium (TEAl) as co-catalyst. The reaction rate of the polymerization of ethylene, as monitored by the increase in the methylene stretching band of the growing polyethylene (PE), has been investigated as a function of the titanium content. After an initial period of mixed kinetics, with the reaction rate significantly higher for the TEAl-modified catalysts compared with the non-modified catalysts, the polymerization proceeded as a pseudo-zero-order reaction with a reaction rate that increased as a function of titanium loading...
June 7, 2016: ChemCatChem
https://www.readbyqxmd.com/read/27812371/combined-operando-x-ray-diffraction-raman-spectroscopy-of-catalytic-solids-in-the-laboratory-the-co-tio2-fischer-tropsch-synthesis-catalyst-showcase
#19
Korneel H Cats, Bert M Weckhuysen
A novel laboratory setup for combined operando X-ray diffraction and Raman spectroscopy of catalytic solids with online product analysis by gas chromatography is presented. The setup can be used with a laboratory-based X-ray source, which results in important advantages in terms of time-on-stream that can be measured, compared to synchrotron-based experiments. The data quality was much improved by the use of a relatively high-energy MoKα radiation instead of the more conventional CuKα radiation. We have applied the instrument to study the long-term deactivation of Co/TiO2 Fischer-Tropsch synthesis (FTS) catalysts...
April 20, 2016: ChemCatChem
https://www.readbyqxmd.com/read/26925172/improved-efficiency-for-partial-oxidation-of-methane-by-controlled-copper-deposition-on-surface-modified-zsm-5
#20
Thomas Sheppard, Helen Daly, Alex Goguet, Jillian M Thompson
The mono(μ-oxo) dicopper cores present in the pores of Cu-ZSM-5 are active for the partial oxidation of methane to methanol. However, copper on the external surface reduces the ratio of active, selective sites to unselective sites. More efficient catalysts are obtained by controlling the copper deposition during synthesis. Herein, the external exchange sites of ZSM-5 samples were passivated by bis(trimethylsilyl) trifluoroacetamide (BSTFA) followed by calcination, promoting selective deposition of intraporous copper during aqueous copper ion exchange...
February 2016: ChemCatChem
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